They're a bunch of assassins. and their clothes look very practical for that.
Why should they care how they look anyway?
Assassins don't normally kill people with just stealth, they kill them with also camoflage and deceit.
This is what the Dark Brotherhood apparel lacks and the fact that it's so obvious that people who see it- should be on high alert.
I would have expected the outfit to identify as a member of the brotherhood, but at the same time: be practical and not stand out.
However such ideals do not seep into the minds of concept artists who create such outfit sets, so we shall never get such armour.
I agree here, the DB clothing is way too obvious. I also very much dislike the tightness of it.
It's not practical in any sense really; you stand out like a sore thumb, you don't have any real storage space on the armour and it doesn't look like it'd even offer much protection in the sense of its construction; the thieves' guild armour is still obvious, but is far more practical-looking.
Definitely agree. And not to mention in a cold climate like Skyrim it'd also lack the furs needed to keep warm while on a chase through the enviroment.
Perhaps in the next TES they'll think 'practical' over design. Pitch black apparel in the middle of an Elsweyr desert would be just plain wrong in so many ways.